7-11
Cisco Unified IP Phone 6901 and 6911 Administration Guide for Cisco Unified Communications Manager 8.5 (SCCP and SIP)
OL-23874-01
Chapter 7 Troubleshooting and Maintenance
Monitoring the Voice Quality of Calls
Step 2 While the phone is powering up, press and hold # button until the Line LED turns green.
Step 3 Release the # button and press 123456789*0#.
The line button LED turns red. The phone reboots when it is finished.
Monitoring the Voice Quality of Calls
To measure the voice quality of calls that are sent and received within the network, Cisco Unified IP
Phones use these statistical metrics that are based on concealment events. The DSP plays concealment
frames to mask frame loss in the voice packet stream.
• Concealment Ratio metrics—Show the ratio of concealment frames over total speech frames. An
interval conceal ratio is calculated every 3 seconds.
• Concealed Second metrics—Show the number of seconds in which the DSP plays concealment
frames due to lost frames. A severely “concealed second” is a second in which the DSP plays more
than five percent concealment frames.
• Mean Opinion Score (MOS) for Listening Quality (LQK) Voice Metrics—Uses a numeric score to
estimate the relative voice-listening quality. The Cisco Unified IP Phones calculate the MOS LQK
based audible-concealment events due to a frame loss in the preceding 8 seconds and includes
weighting factors such as codec type and frame size.
MOS LQK scores are produced by a Cisco-proprietary algorithm, the Cisco Voice Transmission
Quality (CVTQ) index. Depending on the MOS LQK version number, these scores may comply with
the International Telecommunications Union (ITU) standard P.564. (This standard defines
evaluation methods and performance accuracy targets that predict listening quality scores based on
observation of actual network impairment.)
Note Concealment ratio and concealment seconds are primary measurements based on frame loss. A Conceal
Ratio of zero indicates that the IP network is delivering frames and packets on time with no loss.
You can access voice quality metrics remotely by using Streaming Statistics (see the Monitoring the
Cisco Unified IP Phone Remotely chapter).
Using Voice Quality Metrics
When using the metrics for monitoring voice quality, note the typical scores under normal conditions of
zero packet loss and use the metrics as a baseline for comparison.
It is also important to distinguish significant changes from random changes in metrics. Significant
changes are scores that change about 0.2 MOS or more and persist in calls that last longer than
30 seconds. Conceal ratio changes indicate a frame loss greater than 3 percent.
The MOS LQK scores can vary based on the codec that the Cisco Unified IP Phone uses. The following
codecs provide these corresponding maximum MOS LQK scores under normal conditions with zero
frame loss for Cisco Unified Phones 6921, 6941, and 6961:
• G.711: 4.5 MOS LQK
• G.722: 4.5 MOS LQK